1. Field of the Invention
This invention relates in general to an indicator display tube and, in particular, to a novel indicator display tube and to a method for making it.
2. Description of the Prior Art
Generally, Indicator display tubes, which are of the type including a plurality of indicator units mounted inside a transparent envelope for displaying numerals, symbols, letters or the like, have been used with electronic counters and other various indicating devices. One example of such indicator display tubes is the so-called "Nixie" tube in which an anode and a plurality of cathodes are aligned in a stack one above another and the cathodes are selectively energized to provide a display of a desired numeral or letter. Another type of indicator display tube utilizes cathode segments mounted in a common plane and an anode in the form of a wire screen or mesh mounted in a second plane.
For displaying a number containing a plurality of figures with the Nixie tube, it is necessary to employ the same number of Nixie tubes as that of the figures, which inevitably leads to bulkiness of an indicator display device. Accordingly, the Nixie tube is not suitable for such number display. The indicator display tube with cathodes in a common plane is small and thin but requires the same number of leads as used in Nixie tubes. The large number of leads are difficult to form and to lead out of the envelope and results in complexity in the external wiring.
U.S. Pat. No. 3,588,571 discloses an indicator display tube of the type in which many indicator electrode units, each consisting of an anode and a plurality of cathode segments are formed on an insulating plate with the cathode segments in each unit connected in common to those in the other units and connected to common energizing leads but in which the anodes are connected to separate energizing leads which are led out of the envelope. This indicator display tube has advantages in that the number of the leads required is smaller than that of the prior art tubes. However, such tube is likely to provide an incorrect message display because the indicator units are driven on a time sequential basis and the repeating glow discharge causes the ionizable gas, for example argon or neon which is sealed in the envelope, to produce ions which diffuse toward electrodes of adjacent units which lowers the discharge initiating voltage between anode and cathode segments of the adjacent electrode units and causes them to glow.